CHICAGO – An on-duty police officer was fatally shot Tuesday afternoon in downtown Chicago and has been identified as Commander Paul Bauer--a 31-year veteran of the Chicago Police Department.

Cmdr. Bauer, 53, was shot while assisting a tactical team pursuing a fleeing suspect near Thompson Center at 100 W. Randolph Street around 2 p.m. It wasn't immediately clear if the shooting occurred inside or outside the building.

The officer was shot multiple times after he "saw the offender and engaged in an armed physical confrontation," Superintendent Eddie Johnson said.

Johnson said officers initially confronted the suspect because he was acting suspiciously. Police captured the man a short time later, and a gun was recovered at the scene, he said.

There were initial media reports that the man may have been involved in the robbery of a local business, but Johnson did not provide details about what the man was doing that prompted officers to want to speak with him.

Police sources told WGN News that the suspect has a long rap sheet that includes at least one conviction for gun possession and a few for drug dealing.

Cmdr. Bauer was taken to Northwestern Memorial Hospital where he was pronounced dead.

CTA said all buses and trains are running normal near and around the Thompson Center.

The hearts of every Chicagoan are heavy as we mourn the loss of Commander Paul Bauer. Commander Bauer stood for the highest ideals of our police department & our city—to serve & protect the people of Chicago. I ask every Chicagoan to keep his family in their thoughts and prayers. pic.twitter.com/b2lb52fNzZ

18th Dist Cmdr. Paul Bauer - a 31 year veteran of the CPD - was senselessly murdered today while safeguarding Chicago. Cmdr. Bauer was assisting officers in apprehending a suspicious person when he was fatally shot. Person of interest is in custody. pic.twitter.com/lwLGMBY27i